This invention relates generally to a fluid operated power tool and, more particularly, to a fluid control for such a power tool.
Fluid operated power tools have long been employed to set fasteners in a variety of applications. In these fastener setting applications, it is often desirable to control the output of the power tool after the fastener has been set to prevent the tool setting force from exceeding the design limits of the fastener. For example, rotary fluid operated power tools are often utilized to set screws, nuts and other threaded fasteners. For these applications, it is usually desirable to limit the output torque of the tool to meet design specifications of the fastener and workpiece.
Various devices and techniques have been utilized to limit the output of the tool after the fastener has been applied to the workpiece. The simplest method in hand held tools is for the operator to rely on a force output measuring device, for example, a torque indicator, to indicate when the fluid supply to the power tool motor should be shut off.
More sophisticated devices, such as clutch mechanisms, have been employed in rotary power tools to limit output of the tool. Some clutch mechanisms utilize cam and spring or other arrangements to disengage the fluid operated motor from the power output shaft when a predetermined torque load is reached. While these mechanisms have considerable advantages, they are limited in the precision achieved in controlling the maximum torque applied to the fastener because of undesirable kinetic inertial effects of the mechanism. Most such clutches provide a dynamic output disengagement torque which has an undesirable variation from the desired limit.
An improved clutch mechanism was disclosed in U. S. Pat. No. 4,488,604 which eliminated much of the aforementioned inertial effects. This patent disclosed a frictional-contact type clutch in a fluid operated rotary power tool which utilized a latch and pin control unit to shut off the motor when a predetermined output torque, as established at the clutch, was reached. The latch operated within one revolution of relative clutch slippage to release a pin which shuts off the fluid supply to the motor.
Variation in desired set torque can be determined by statistical analysis of repeated measurements to calculate the standard variation from the mean, i.e., the desired set torque. In automotive applications it is common to measure performance by plus-or-minus three times the standard deviation, i.e., the so called "six-sigma" standard. The best six-sigma combined fastening performance of prior art fluid operated rotary power tools under ISO standard 5393 has generally been no better than about plus or minus 20 percent of mean torque.
Bearing in mind these and other deficiencies of the prior art, it is therefore an object of the present invention to provide a fluid operated power tool with improved force disengagement control.
It is also an object of the present invention to provide such a tool with a force disengagement control which reduces variations in fastener setting force in repeated applications.
It is a further object of the present invention to provide such a tool which can be hand held.
It is another object of the present invention to provide a fluid operated power tool which has a rotary output and improved torque disengagement control.
Other objects will be in part obvious and in part pointed out in more detail hereinafter.
A better understanding of the objects, advantages, features, properties and relations of the invention will be obtained from the following detailed description and accompanying drawing which sets forth an illustrative embodiment and is indicative of the way in which the principle of the invention is employed.